Various methods of simultaneously measuring moisture and density of various materials have been proposed. In a widely used sampling method, data differs when samples are taken from different parts, and the results cannot be immediately known. Therefore, simultaneous measurement of density and moisture continuously in on-line manner, instead of the aforementioned sampling method, has been suggested. One example of such method is shown in, for example, FIG. 1.
Referring to FIG. 1, in an on-line measuring apparatus for measuring a bulk material, a first radiation source 29 (for example Cf-252) and a second radiation source 30 (for example Cs-137) are provided on the way of feeding of the object (for example, coke) on a belt conveyer. Radioactive rays emitted from the first and second radiation sources 29 and 30 and passed through the object 20 are detected by a detector. In order to measure simultaneously the density and the moisture content of object 20 on-line, it was necessary to provide in the detector a density meter 27 formed of an NaI scintillator, for example for detecting gamma ray, and a moisture meter 28 formed of a glass scintillator, for example, for detecting fast neutron ray. Outputs from these scintillators were separated by a pulse height discriminating circuit (PHD circuit) in accordance with a pulse height discriminating method utilizing spectral characteristics, whereby respective data of measurement were provided.
However, simultaneous measurement of one object 20 by using two different meters 27 and 28 requires much space for arranging respective meters, and maintenance of these meters is troublesome.
In order to solve these problems, use of phoswich detector including an NaI scintillator and a plastic scintillator has been proposed. An example is disclosed, for example, in Japanese Patent Laying-Open No. 2-74890.
According to this article, outputs from two different scintillators are received by a photomultiplier (hereinafter referred to as a PM) and amplified by a pulse amplifier. In this case also, a PHD circuit is used.
However, according to this method, pulse-height distribution of the gamma ray pulses detected by the NaI scintillator and that of neutron ray pulses detected by the plastic scintillator cannot be separated well dependent on the height of the pulses, which prevents stable analysis.
In order to provide stable result of analysis, use of a liquid scintillatot with pulse shape discriminating method has been proposed. Combination of a PSD (Pulse Shape Discrimination) circuit and a liquid scintillator brings about an advantage that fast neutron ray can be discriminated from gamma ray. However, a liquid scintillator is difficult to handle, since it is mechanically fragile and inflammable. In addition, practical application is difficult, except for study in laboratories, since it is very expensive.
The present invention was made to solve the above described problems, and its object is to provide a density-moisture meter allowing easy handling and easy analysis.
Another object of the present invention is to provide a density-moisture meter employing a phoswich detector which enables effective and stable measurement.
A further object of the present invention is to provide a density-moisture meter which can be applied to general field of industry.
A still further object of the present invention is to provide a method of industrial measurement of density and moisture allowing ready analysis.